A district is as stable and grounded as its superintendent, according to some leaders and education experts. And given findings in a recent report from the Council of the Great City Schools (CGCS), which specifically states that the average tenure of urban superintendents increased from 2.3 years in 1999 to 3.6 years in 2010, an increase of 56 percent, educators across the nation are celebrating. Specifically, longer superintendent tenure has a positive effect on student achievement, according to research by McREL, a nonprofit research group based in Denver. It found a positive correlation between longevity and academic achievement. District leaders who focus on the right goals, manage change effectively and stick around long enough to see results tend to have higher-performing students. In this article, "District Administration" editors look back over 15 years at the tenure of the men and women who have led the 10 largest districts in the nation.